DNA amplification is a process of replicating a target double-stranded DNA (dsDNA) to generate multiple copies. Since individual strands of a dsDNA are antiparallel and complementary, each strand may serve as a template strand for the production of its complementary strand. The template strand is preserved as a whole or as a truncated portion and the complementary strand is assembled from deoxyribonucleoside triphosphates (dNTPs) by a DNA polymerase. The complementary strand synthesis proceeds in the 5′→3′ direction starting from the 3′ terminal end of a primer sequence that is hybridized to the template strand. A variety of efficient nucleic acid amplification techniques are currently available such as polymerase chain reaction (PCR), ligase chain reaction (LCR), self-sustained sequence replication (3SR), nucleic acid sequence based amplification (NASBA), strand displacement amplification (SDA), multiple displacement amplification (MDA), or rolling circle amplification (RCA). Many of these techniques generate a large number of amplified products in a short span of time.
Whole-genome amplification (WGA) involves non-specific amplification of a target DNA. WGA is often achieved by MDA employing random oligonucleotide primers (e.g., NNNNN*N) for priming DNA synthesis at multiple locations of the target DNA along with a high fidelity DNA polymerase having a strand displacing activity (e.g., Phi29 polymerase). Even though currently available commercial WGA systems such as GenomiPhi (GE Healthcare, USA) and RepliG (Qiagen) kits provide optimal results with an input DNA of 1 nanogram or more, performance of these systems is poor when the target DNA is available only in smaller quantities or when amplification of DNA from a few or single cells is performed.
Despite these advancements, there remains a need for developing more efficient whole-genome nucleic acid amplification methods that have lower bias in terms of sequence coverage and produce lower levels of non-specific, background amplification. Amplification of trace amounts of target DNA using conventional methods often results in incomplete amplification of DNA sequences leaving “dropouts” in sequence coverage and amplification bias wherein DNA sequences are amplified unevenly. Further, products of the amplification reaction (amplicons) may often anneal among themselves leading to the generation of undesirable chimeric products. Efficient methods for non-specifically amplifying trace amounts of target DNA are therefore highly desirable.